Are 340’s rare

Yeah well rpm ain't everything to a streeter. example;
7500 in first gear(TF) with 3.23s comes to 68mph. Did I say still in First gear?
With a power-peak near 7000, what cam do you run, and how's that gonna run in Drive at 30 mph?
No thanks.
I'll take the 408, or 388 (4.04 x 3.79), or even an HO367, with a power-peak around 5400 give or take.
But I gotta say this;
a super-Hi-Compression 340, with a 318 cam, makes a chitload of Bottom-End torque, which is just right for a streeter with 3.23s, or even, a lil less.

I used to get so much flack for having a 360-based small-block. Since it's a 4.04 x 3.58, I started calling it a stroked 340, and that was the end of the criticisms.